1. Field of the Invention
The present invention relates to a hand provided as an end effector in a robot. The invention also relates to a handling robot equipped with such a hand.
2. Description of the Related Art
Hands having various configurations, each of which is attached, as an end effector, to the end of a robot arm, are known. The conventional hands can be roughly classified, in terms of the mechanical configuration thereof, into three types; such as a mechanical hand including a plurality of (generally, two or three) rigid fingers for gripping an object having a specified shape, a specific hand for holding an object having a specified structure by vacuum or magnetic adsorption, and a multi-finger hand (or a universal hand) for gripping an object having an optional shape by various operations of a plurality of (generally, two to five) finger mechanisms, each having a joint.
Also, a robot (generally referred to as a handling robot) using a hand attached to the end of an arm and carrying out various handling works for workpieces, such as loading/unloading, palletizing/depalletizing or pick-and-place, is known. For example, Japanese Unexamined Patent Publication (Kokai) No. 7-332944 (JP-A-7-332944) discloses a handling robot performing a handling work for a cast product placed on a pallet by using a mechanical hand including two parallel openable/closable fingers. JP-A-7-332944 also discloses a crane apparatus by which a coil for steel-manufacturing use, placed in a coil yard, is lifted and transported with a vertically movable hook member.
Among various types of hands described above, the mechanical hand is comparatively simple in configuration and easy to control and, therefore, tends to be widely used for the handling robot. In the conventional mechanical hand, however, the shape of the rigid fingers and the gripping operation mode thereof are configured to be adaptable to the attributes of a specified object to be gripped, such as dimensions, shape and weight, so that it is generally difficult to grip objects having different attributes by a mechanical hand having a common structure.
Also, it is sometimes difficult, for the handling robot equipped with the mechanical hand (as described in, e.g., JP-A-7-332944), to pick out a desired workpiece from a plurality of workpieces having the same attribute, which are randomly placed in various orientations in a pallet or container. Generally, the workpieces randomly placed (e.g., stacked-up) assume a variety of orientations different from an orientation desired by the robot, so that, even when the arm is variously operated, the interference between the hand or arm and the surrounding objects such as other workpieces may occur, which may make it difficult to grip a predetermined grippable portion of the workpiece. In an attempt to grip each workpiece on a portion thereof able to be actually gripped, the hand is required to be changed to the other one having a structure corresponding to the actually grippable part at every time of gripping, which results in an increased cost and cycle time for a handling work.
On the other hand, the crane apparatus, such as that described in JP-A-7-332944, can operate to scoop up an object (or a coil) with a hook member, so that it is not required to set a specified grippable portion on the object to be transported. In some applications, therefore, it is facilitated to pick out a desired object from a plurality of randomly placed objects, in comparison with a picking work by a robot having a mechanical hand. However, the object scooped up by the hook member is not stably held on the hook member, so that it is required to maintain a transporting speed at slow rate, so as to prevent the object from falling off. Further, as compared with the mechanical hand, it is difficult for the hook member to accurately position and place an object at a predetermined location.